Ask Well | Can Pets Spread Ebola?

Q. I’m flying soon. What is the risk of contracting Ebola on a flight?

A. Not high. Top Ebola experts have said they would not expect to be infected even if they were sitting next to another passenger with Ebola – unless that passenger actually vomited or bled on them. Patrick Sawyer, the Liberian-American who brought the virus to Nigeria in July, was so sick he had to be helped off the plane in Lagos. He had vomited while on board. There were about 200 passengers on the plane, according to Nigerian health authorities, and not one of them got infected.

Q. Isn’t the virus airborne if a sneeze can move it three feet? What is the likelihood that Ebola will mutate into an airborne virus?

A. Although both the World Health Organization and the Centers for Disease Control and Prevention take the position that Ebola is not transmitted through the air, scientists are publicly battling, on news websites and science websites over whether it is possible in rare cases — or could become possible if the virus mutates.

Much has been made of two small studies in which the virus appeared to have passed through the air between monkey cages or between pigs and monkeys caged above them. It does appear, some scientists argued, as if prolonged exposure to airborne droplets under laboratory conditions might pass the disease. However, others argued that transmission might be an accident of cage cleaning, feeding or urine splashes.

Also, in 1989, 100 rhesus monkeys shipped from the Philippines to a government research lab in Reston, Va., started an outbreak of a variant of Ebola that does not harm humans. Ultimately, to stop the outbreak, all 600 monkeys in the building were killed. Some scientists who worked there believe the virus spread between cages and perhaps even between rooms when monkeys sneezed or coughed.

There are two kinds of airborne transmission. An infectious dose of measles, smallpox or chickenpox virus can be contained in a droplet small enough to hang in the air, so the next person to walk through that “sneeze cloud” catches it, or the disease transmits through ventilation systems. Influenza is thought to need bigger doses in larger droplets that fly as far as six feet but then fall to the floor.

No human airborne transmission of Ebola has been confirmed, even though there have been multiple outbreaks in Africa since 1976, and many crowded places – like minibus taxis – providing opportunities.

If Ebola was transmitted like influenza, experts point out, an outbreak would echo the spread pattern of the 2009 flu pandemic, and by now there would be millions of cases around the globe.

Ebola does not typically cause sneezing or coughing and saliva does not normally build up large viral loads until late in the disease. But because patients can cough vomitus or blood, or vomit violently, caregivers routinely wear masks and goggles.

No one can say exactly what the likelihood is that the virus will mutate to definitively become airborne, but it is not thought likely. No virus has ever been known to change its mode of transmission. H.I.V. mutates incredibly rapidly — as much in one day as flu does in a year, according to C.D.C. scientists, and H.I.V. has not become airborne.

Since Ebola is good at finding hosts, it is under no great Darwinian pressure to change. On the contrary, since human Ebola victims die so fast that they can’t spread it to many others, the more likely change is for the virus to become milder so victims live longer.

Airborne viruses have surface proteins that attach to cells in the nose and throat. Imagine throwing magnetized BB’s into a cast-iron pipe; all would stick. Ebola, lacking those proteins, is like marbles, falling down the pipe into the gut, where it attaches. It may take a lot of mutation to do the equivalent of changing a marble into a magnetic BB.